Diabetic Lumbosacral Radiculoplexus Neuropathy

Diabetic lumbosacral radiculoplexus neuropathy (diabetic amyotrophy) is a subacute, painful, asymmetric lower limb neuropathy with proximal weakness and weight loss, due to microvasculitis of the lumbosacral plexus and roots. It occurs mainly in type 2 diabetes aged over 50 years, often with well controlled or recently diagnosed diabetes. Non-diabetic forms exist.

Pathophysiology. Immune mediated microvasculitis causes ischaemic injury to the nerve roots, plexus and proximal nerves.

Sudden severe pain in the hip, thigh or buttock (often nocturnal), followed within days to weeks by weakness and wasting of the quadriceps, hip flexors and adductors, with absent knee jerk, and later distal and contralateral spread. Weight loss of over 10 kg is common, and autonomic symptoms occur. Improvement is slow over 1 to 3 years, with incomplete recovery.

Red flags.

• Rapid progression of weakness or bilateral involvement.
• Fever, back pain or bowel and bladder disturbance suggesting another cause.

Clinical diagnosis with electromyography showing patchy lumbosacral denervation with paraspinal involvement. MRI of lumbosacral spine and plexus excludes compression and tumour. Check HbA1c, ESR, CRP, vitamin B12, protein electrophoresis, antinuclear antibodies, ANCA, and renal and thyroid function. CSF protein is raised. Nerve biopsy is reserved for atypical cases.

Differential diagnosis.

• Lumbar radiculopathy and spinal stenosis, cauda equina syndrome.
• Femoral neuropathy, retroperitoneal haematoma and tumour.
• CIDP, vasculitic neuropathy and Guillain-Barre syndrome.

Glycaemic control. Optimise diabetes, with caution to avoid rapid correction (treatment induced neuropathy). Avoid hypoglycaemia.

Immunotherapy. Evidence is limited. Corticosteroids (prednisolone 60 mg daily for 1 to 2 weeks, tapered over 6 to 12 weeks, or methylprednisolone 1 g IV daily for 3 to 5 days) may shorten the painful phase and speed recovery in selected patients, but have not shown clear benefit on weakness. Intravenous immunoglobulin 0.4 g/kg daily for 5 days has been used. Monitor glucose closely during steroids.

Pain. Gabapentin 300 mg three times daily, increased to 600 to 1200 mg three times daily (adjust to eGFR), pregabalin 75 to 300 mg twice daily, duloxetine 60 mg daily, or amitriptyline 10 to 75 mg at night. Opioids for severe pain, for short periods.

Rehabilitation. Physiotherapy, walking aids, knee brace and falls prevention, nutrition support and treatment of depression.

Monitoring. Pain, strength, weight and glycaemic control.

Referral and escalation. Refer to neurology and diabetes services.